Persistence of Antimicrobial-Resistant Bacteria on Hospital Surfaces Varies: Presented at ASM Microbe

By Brian Hoyle

ATLANTA -- June 12, 2018 -- Acinetobacter baumannii and carbapenemase-producing Klebsiella pneumoniae could persist in a viable but non-culturable state, which could allow them to evade infection control strategies that reply on swab sampling, while perhaps retaining their pathogenic punch, according to a study presented here at ASM Microbe 2018.

“Our results suggest that both pathogens survive long enough for potential transfer to occur from surfaces to patients if disinfection practices are not thorough,” wrote Amanda Lyons, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, and colleagues in their presentation.

The results of the study showed that persistence varies between organisms and can be dependent on temperature and relative humidity.

Surfaces can harbour bacteria in hospitals and elsewhere. Surprisingly, however, the persistence of disease-causing bacteria on hospital surfaces remains unclear.

For the current study, following culture, the bacteria were suspended in a fluid that simulated body fluid and were then dispensed on coupons made of stainless steel (to mimic the grab-bars that are part of hospital beds) and plastic (to mimic countertops). The coupons were incubated at 26 degrees Celsius and 57% relative humidity or 18 degrees Celsius and 20% relative humidity for 28 days. During that time, viable counts were done and metabolic activity was gauged by measuring esterase activity in a fluorescence assay.

A baumannii survived for 28 days with virtually no change in viable count or esterase activity for both culture conditions on stainless steel and plastic. In contrast, the viable counts of K pneumoniae declined steadily with time for both culture conditions on both surfaces.

By day 6 at 26 degrees Celsius and 57% relative humidity, reductions in viable count of 5 log10 and 6 log10 were recorded on plastic and steel surfaces, respectively. However, esterase activity did not decline nearly as precipitously with time, with only by 1 log10 reduction on either surface. At 18 degrees Celsius and 20% relative humidity, K pneumoniae survived longer; however, the decline after 21 days on both surfaces was 5 log10. Esterase activity displayed only a 1 log10 decline over the same period.

The findings for K pneumoniae were interpreted as evidence that the bacteria were still alive but incapable of growth and division -- the viable but non-culturable state.

The finding of persistence in a dormant state for K pneumoniae is troubling. But, the possible consequences for patients remain unclear.

“We do not know the virulence of these pathogens when viable but non-culturable, and more studies are needed to determine whether they remain a potential risk to patients in this state,” the authors concluded.

ASM Microbe is the joint meeting of the American Society for Microbiology and the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

[Presentation title: Persistence of Antimicrobial Resistant Bacteria on Hospital Surfaces: Effect of Relative Humidity and Temperature. Abstract SUNDAY-CIV LB2]

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